Vehicles with braking force retaining means are known. The braking force retaining means enables continuous braking force retention after releasing the brake pedal. For example, Japanese Laid-open Patent Publication No.9-202159 discloses a vehicle having such braking force retaining means. In this vehicle, driving force is controlled to be weak while the break pedal is depressed, and when the brake pedal is released, the driving force is controlled to be strong in order to start the vehicle. Further, because of difficulty in starting the vehicle while retaining braking force as well as occurrence of brake dragging after starting, as shown in FIG. 12, control is made such that the braking force is immediately released as soon as the starting driving force increases to the greater condition. The vehicle disclosed in this publication detects whether or not driving force increases from the weak driving force condition, in which driving force of the starting clutch is controlled to be weak, to the strong driving force condition, in which driving force increases by way of releasing the brake pedal. The vehicle continues to retain braking force until switching to the strong driving force condition is detected, and releases the braking force retained when such a switching operation is detected. With the control of releasing the braking force retained, unnecessary driving force is not required while the vehicle stops, and a smooth starting operation is achieved without brake dragging.
As shown in FIG. 12, however, if braking force is instantly released when the starting driving force increases to the strong driving force condition, the driver often experiences a sudden start of the vehicle. This is more prominent on a down slope since the vehicle's own weight additionally affects on the driving force of the vehicle per se. The driver recognizes such a sudden start as an impact or brake dragging.
The present invention seeks to provide a braking force control unit which eliminates a sudden start of the vehicle, and achieves a smooth starting operation of the vehicle.